Frequency-Domain Photon Migration (FDPM) is a non-invasive optical technique which utilizes near-infrared light to monitor physiology in bulk tissues. Optical properties derived from FDPM measurements can be used to construct low-resolution functional images and, consequently, provide a relatively low-cost adjunct to many conventional diagnostic tools. Considerable interest has been generated in applying FDPM to tumor imaging; however, relatively little is known about in vivo tissue optical properties and their relationship to physiology. Since optical properties (absorption and scattering parameters) are the fundamental determinants of contrast in FDPM-derived images, we will employ the LAMMP 1 GHz FDPM instrument to characterize optical properties in various types of normal and malignant tissues in vivo. We believe this information is essential for realistically estimating the feasibility of tumor optical imaging.